Composite soft magnetic material

Abstract

A composite soft magnetic material is produced from soft magnetic metal (e.g., Sendust) particles by coating the particles with a non-magnetic metal oxide (e.g., α-alumina) in a mechano-fusion manner, or heat treating the particles to form a diffusion layer of α-alumina thereon, coating the coated particles with a high resistance soft magnetic substance (e.g., ferrite), and sintering the double coated particles under pressure as by hot pressing or plasma activated sintering. It exhibits high saturation magnetic flux density, magnetic permeability, and electric resistivity. The non-magnetic metal oxide intervening between the soft magnetic metal and the high resistance soft magnetic substance is effective in reducing core loss.

We claim: 
     
       1. A composite soft magnetic material comprising soft magnetic metal particles having a mean particle diameter of 5-100 μm and a coercive force of up to about 0.5 Oe as measured in bulk form,   a layer of high resistance soft magnetic substance having an electric resistivity of about 10 2  Ω-cm or higher intervening between the particles, and   a layer of non-magnetic metal oxide intervening between each soft magnetic metal particle and the high resistance soft magnetic substance layer;   wherein said material has a core loss of about 350-3,000 kW/m 3  at 0.1 mT, 100 kHz and about 5-100 kW/m 3  at 0.1 mT, 10 kHz.   
     
     
       2. The composite soft magnetic material of claim 1 which is obtained by sintering under pressure said soft magnetic metal particles and said high resistance soft magnetic substance with said non-magnetic metal oxide intervening therebetween. 
     
     
       3. The composite soft magnetic material of claim 2 which is obtained by coating the soft magnetic metal particles with the non-magnetic metal oxide and further with the high resistance soft magnetic substance, and sintering the coated particles under pressure. 
     
     
       4. The composite soft magnetic material of claim 3 wherein the step of coating the particles with the high resistance soft magnetic substance is carried out by a mechano-fusion process including applying mechanical energy to the particles. 
     
     
       5. The composite soft magnetic material of claim 3 wherein the non-magnetic metal oxide coating is 0.02 to 1 μm thick. 
     
     
       6. The composite soft magnetic material of claim 2 which is obtained by heat treating the soft magnetic metal particles in an oxygen atmosphere, thereby forming a diffusion layer of non-magnetic metal oxide on the particle surface, coating the particles with the high resistance soft magnetic substance, and sintering the coated particles under pressure. 
     
     
       7. The composite soft magnetic material of claim 6 wherein the soft magnetic metal particles contain at least one member of Al and Si. 
     
     
       8. The composite soft magnetic material of claim 6 wherein the non-magnetic metal oxide diffusion layer is 3 to 300 nm thick. 
     
     
       9. The composite soft magnetic material of claim 6 wherein the non-magnetic metal oxide is at least one oxide selected from the group consisting of Al and Si. 
     
     
       10. The composite soft magnetic material of claim 3 or 6 wherein the high resistance soft magnetic substance coating is 0.02 to 10 μm thick. 
     
     
       11. The composite soft magnetic material of claim 6 wherein the step of coating the particles with the high resistance soft magnetic substance is carried out by a mechano-fusion process including applying mechanical energy to the particles. 
     
     
       12. The composite soft magnetic material of claim 2, 3 or 6 wherein the sintering step is hot press sintering or plasma activated sintering. 
     
     
       13. The composite soft magnetic material of claim 2, 3 or 6 wherein the sintering under pressure is followed by heat treatment in an oxygen atmosphere. 
     
     
       14. The composite soft magnetic material of claim 1, wherein said high resistance soft magnetic substance has a mean particle size of about 0.01-2 μm. 
     
     
       15. A composite soft magnetic material comprising soft magnetic metal particles having a mean particle diameter of 5-100 μm and a coercive force of up to about 0.5 Oe as measured in bulk form, a layer of high resistance soft magnetic substance having an electric resistivity of about 10 2  Ω-cm or higher and a mean particle size of about 0.01-2 μm, and   a 0.02-1 μm thick layer of non-magnetic metal oxide intervening between each soft magnetic particle and said high resistance soft magnetic substance layer;   wherein said material has a core loss of about 350-3,000 kW/m 3  at 0.1 mT, 100 kHz and about 5-100 kW/m 3  at 0.1 mT, 10 kHz.   
     
     
       16. A composite soft magnetic material comprising soft magnetic metal particles having a mean particle diameter of 5-100 μm and a coercive force of up to about 0.5 Oe as measured in bulk form,   a layer of high resistance soft magnetic substance having an electric resistivity of about 10 2  Ω-cm or higher and a mean particle size of abut 0.01-2 μm, and   a 3 to 300 nm thick layer of non-magnetic metal oxide formed by diffusion intervening between each soft magnetic particles and said high resistance soft magnetic substance layer;   wherein said material has a core loss of about 350-3,000 kW/m 3  at 0.1 mT, 100 kHz and about 5-100 kW/m 3  at 0.1 mT, 10 kHz   wherein said composite material is obtained by heat treating said soft magnetic metal particles in an oxygen atmosphere, thereby forming a diffusion layer of non-magnetic metal oxide on said particle surface, coating said particles with said high resistance soft magnetic substance and sintering said coated particles under pressure.